Lou: Yes, the Holocaust changed everything. I grew up knowing but I'm still floored by the vast numbers. Towns that used to be strongly Jewish with no Jews left anymore. Cities that used to be a third or more Jewish with a handful left now.
But there were survivors. People who scrambled and made it to other countries outside the war zones. People who stayed and made a new life for themselves in a different part of Europe. And children separated from their families and brought up without them.
If your friend doesn't want to test because he thinks it's not worth it, then yes I'd urge him to. Because his parents were young when they survived and there are likely family members they lost touch with. But if he doesn't want to test because it's emotionally overwhelming, I can understand that.
Most of my family survived (my mom got out of Hungary in 1939, the rest of my direct ancestors left Europe earlier). Some stayed and survived. Some stayed and didn't. But I still find it all overwhelming at times, even though I was born long after the war. Even though my mom was a small child when she left with her parents. Remember, your friend grew up with two concentration camp survivors. That is a completely different experience from what most American Jews have had (or Jews from other non-European countries and even some in Europe).
Poland was hit really hard. My grandfather is from Warsaw and he and his family came to the US just before and after WWI (they were separated). But I hear both his parents had siblings who went all over the world, I just don't know how to find them (my family members who have told me don't remember enough details and my grandparents and great aunts/uncles are all gone).